German Patent 35 31 632 teaches a radial piston engine comprising a housing, an annular cam disk fixedly mounted in said housing, a cylinder block rotatably mounted about an axis and with respect to said cam disk, a plurality of bores arranged in said cylinder block radially with respect to said axis of rotation, a plurality of pistons respectively mounted in said bores, and cylindrical rollers for supporting said pistons on said cam disk, said rollers having axes which extend parallel to the axis of rotation of the cylinder block, and wherein said bores of said cylinder block which are adapted to receive said pistons are provided with recesses in the area of movement of said rollers, so as to receive sections of said rollers on both end faces of said rollers.
In said known radial piston engine the circumferential grooves require a certain depth, so as to allow an insertion of said rollers into said bores which are adapted to receive said pistons, while at the same time the rollers are guided sideways (on their side) at remaining or abuttment surfaces of the sideways arranged rotor or cylinder block wall. So as to achieve this goal, a relativly large depth is required for the circumferential grooves. This causes a reduction or weakening of the segment which remains between two piston bores. Such segments are necessary for supporting each piston. Said segments are subject to bending forces during operation due to the effect of the piston force. Thus the danger of a breakage exists, particularly a breakage due to extended periods of operation.
It is an object of the present invention to design a radial piston engine of the type mentioned above in such a manner that the disadvantages of known engines of this type are avoided. It is a particular object of the invention to design a radial piston engine of the above mentioned type in such a manner that the dangers of breakage in general or breakage due to extended periods of operation are avoided.
In accordance with the present invention a piston engine of the type mentioned above is provided with recesses formed in the following manner:
1. at the outer circumference of the rotor circumferential grooves are provided which cut through the piston bores in their radially outer area and PA0 2. recessions (zones free of material) are provided radially inwardly with respect to the circumferential groove.
Due to the fact that the depth of the circumferential grooves is reduced by half with respect to the prior art, and in addition by providing in the area of the bores recessions (zones free of material), by milling, or, alternatively, by providing kidney-shaped openings, the desired insertion of the roller is maintained, wherein at the same time the supporting cross-section of the remaining segment in the cylinder block supporting the pistons remains sufficiently large.
In case said zones free of material are formed by milling, no great amount of work or cost is involved, in as much as modern machining centres provide for the additionally required milling operation without requiring a renewed clamping or mounting operation for the work piece. Only a small amount of material has to be removed, a fact which is beneficial with regard to the strength of the cylinder block.